The present invention relates to a technique for detecting a pitch (or fundamental frequency) of an audio or sound signal.
Heretofore, there have been proposed various techniques for detecting a pitch of an audio or sound signal. Japanese Patent Application Laid-open Publication No. SHO-61-26089 discloses an example technique, where detection is made of a pitch of a sound signal having passed through a low-pass filter and where the cutoff frequency of the low-pass filter is variably controlled in accordance with a result of the pitch detection. The pitch detection technique disclosed in the No. SHO-61-26089 publication can advantageously detect a pitch of a sound signal with a high accuracy because, of the sound signal, intensities of peaks other than a peak corresponding to the pitch are controlled.
However, with the technique disclosed in the No. SHO-61-26089 publication, where the cutoff frequency of the low-pass filter is changed instantaneously to a frequency corresponding to the detected pitch of the sound signal at a predetermined time point after the pitch detection, pitches detected before and after the change of the cutoff frequency tend to become unstable.